The control and mechanism of secretion of ACTH and endorphin will be studied using a mouse pituitary tumor cell line (AtT-20/D-16V) and primary suspensions of rat anterior and intermediate pituitary cells. Cells will be incubated with radioactive amino acids for a sufficient time to achieve a steady labeling pattern for most of the hormone pools in the cells. Established immunochemical procedures will be used to isolate ACTH-containing and endorphin-containing molecules secreted in response to a variety of secretagogues and agents which block secretion. The electrophysiological events which accompany these changes in secretory rate will be monitored by intracellular recordings. In this way, the control of secretion of different peptide regions of the pro-ACTH/endorphin common precursor will be investigated in cells from several different tissues.